Question

I have a class “ABC” and its method which returns non autoreleases object of that class.

@interface ABC:NSObject
+(ABC *)aClassMethodReturnsObjectWhichNotAutoreleased;
@end  

@implementation ABC
+(ABC *)aClassMethodReturnsObjectWhichNotAutoreleased{
   ABC *a = [[ABC alloc]init];
   return a;
}
@end

If I have a protocol Foo.

@Protocol Foo
@required
-(void)abc;
@end

My ABC class is “not” confirming Foo protocols.

1st call

id<Foo> obj = [ABC aClassMethodReturnsObjectWhichNotAutoreleased]; //show warning

It shows warning “Non Compatible pointers..” thats good.Abc did not confirm protocol Foo

BUT
2nd call

id<Foo> obj = [NSArray arrayWithObjects:@"abc",@"def",nil]; // It will "not" show warning as it will return autorelease object.NSArray don't confirm protocol Foo

In first call compiler gives warning and in second call compiler is not giving any warning.I think that is because i am not returning autorelease object.

Why is compiler not giving warning in 2nd call as NSArray is also not confirming FOO
Thanks in advance

Answer 1

In your first example, the return value is a specific type so the compiler can verify the assignment.

In the second example, the NSArray arrayWithObjects: method has a return type of id. You can assign an object of type id to a variable of any type. The compiler has no way to verify that what you are doing is truly correct or not.

This issue has nothing to do with autoreleased objects. It’s all about the data types. id is a kind of catch-all type that can be anything.